When data transmission is performed in an existing LTE system, one subframe is usually used as a basic transmission time interval (TTI), with a time length of 1 millisecond. Each subframe may be divided into two timeslots. Each timeslot includes seven orthogonal frequency division multiplexing (OFDM) symbols (corresponding to a normal cyclic prefix). In other words, one subframe includes 14 OFDM symbols. In an LTE downlink time-frequency resource, the first one to four OFDM symbols of a subframe are usually specified as a control region (Control Region), and a base station sends downlink control information (DCI) in the control region to perform uplink or downlink scheduling. In existing LTE, a physical downlink control channel (PDCCH) may be used to carry the DCI at a physical layer. In some implementations, the PDCCH includes one or more control channel elements (CCEs), and a quantity of CCEs included in a PDCCH is usually represented using an aggregation level. A CCE resource set used by a user terminal to perform PDCCH blind detection (Blind Detection) is referred to as a PDCCH search space (search space). Currently, when mapping a PDCCH in a subframe, the base station determines, based on a channel status of UE, an aggregation level used for the PDCCH, and performs mapping in a search space corresponding to the aggregation level. Each aggregation level is corresponding to one search space.
To reduce a transmission delay in a data communication process, the 3rd Generation Partnership Project (3GPP) considers reducing a conventional TTI whose length is 1 millisecond to a short TTI (sTTI) with one to seven symbols. Because a short TTI structure is used, a quantity of symbols of a TTI is reduced, but a quantity of OFDM symbols used to send the DCI remains unchanged, causing a larger proportion of resource overheads occupied by the PDCCH that carries the DCI. To reduce overheads of the PDCCH, in some implementations, a self-contained channel sending method in which the PDCCH is embedded, for sending, into a physical downlink shared channel (PDSCH) for sending data is used, and frequency domain interleaving is performed on the PDCCH control channel on a known time-frequency resource block, to reduce resource overheads. A PDCCH time-frequency resource domain is preset in a time-frequency resource domain of the PDSCH.
However, when the base station sends the downlink control channel to the UE using the self-contained channel sending method, a time-frequency resource in the preset PDCCH time-frequency resource domain is not necessarily occupied totally, causing time-frequency resource waste.